Intrusion detection systems

ABSTRACT

A system for sensing seismic and magnetic disturbances, comprising a segmented transducer, such as a line sensor, and electronic circuitry for processing the signals developed by the segmented transducer. The segmented transducer comprises sets of windings wrapped around a ferromagnetic core. Currents are induced in transducer windings as a result of magnetostriction when seismic disturbances or stresses cause strains in the ferromagnetic core. Currents are also induced in the transducer windings by magnetic field disturbances caused by external ferrous objects. Electronic signal processing circuitry associated with the transducer extracts information from the induced seismic and magnetic signals and activates an alarm if the information meets predetermined criteria. Important criteria used include whether the seismic signals are impulsive, whether the magnetic or stress disturbances are localized, and whether specific thresholds of magnetic and stress activity are reached.

United States Patent Erdmann et al.

Nov. 5, 1974 INTRUSION DETECTION SYSTEMS Inventors: Dav

id P. Erdmann, Hopkins; Dennis Assigneel Honeywell, -5 MinneaP01iS,MinnA system for sensing seismic and magnetic disturb- [22] Filed: June 81973 ances, comprising a segmented transducer, such as a line sensor,and electronic circuitry for processing the PP Noel 368,162 signalsdeveloped by the segmented transducer. The segmented transducercomprises sets of windings [521 [LS CL 340/258 D 324/3, 340/258 C,wrapped around a ferromagnetic core. Currents are 340/261 induced intransducer windings as a result of magneto- [51] Int. Cl. G08b 13/24fiction when seismic disturbances of Stmsses Cause [58] Field of Search340/258 R 258 C 258 D strains in the ferromagnetic core. Currents arealso in- 340/261 L; 3124/3 duced in the transducer windings by magneticfield disturbances caused by external ferrous objects. Elec- [56]References Cited tronic signal processing circuitry associated with theUNITED STATES PATENTS transducer extracts information from the inducedseismic and magnetic signals and activates an alarm if the 3,543,221l1/l970 Burney 340/258 R i f ti meets d t i d it i I t t g 232 55criteria used include whether the seismic signals are 3634843 1 H972gifi a 340,258 C impulsive, whether the magnetic or stress disturbances3696369 10/1972 g' g 'i 340/258 D are localized, and whether specificthresholds of mag- 317171864 2/1973 Cook et al. 340/2523 D netic andStress activity are reached- 3,737,768 6/1973 Lazenby et al. 324/3 L3,745,552 7/1973 Wilt 340/258 D 12 Clam, 9 Drawmg Flgures F r r F 56|slm| SAMPLED l TIME BETWEEN j AVERAGE A zx r n ic ron 5 H) SEISMIC m m1 I I F46 MAXIMUM I 32 [mm AVERAGER SELECTOR RESET N P 'l a 0 58 2 I i rBCR CONTROL 44 ARRAY AND OUTPUT ls (HI P2 'EXTRACTOR COMBINATION CIRCUlT2 SAMPLED ABR LOG:

AVERAGER A82 2 AMP. 12 mzm 2 1 [4s 64 as A' A (kl L RM m2 AVERAGER Am IMAGNZTIC f 2r:ua%: HT SELECTOR LT p i a SAMPLED 3 E Av RAeER 5 m AMP. ssm it l 3 lm (t )l r46 3 ,AvERAeER Am Primary ExaminerDavid L. Trafton[57] ABSTRACT PATENIEDNBY 5 mm 3846L790 SHEET '4 BF 9 FIG.4

INTRUSION DETECTION SYSTEMS BACKGROUND OF THE INVENTION This inventionpertains to intrusion detection systems, particularly intrusiondetection systems which utilize a segmented sensor or plurality ofsensors which are sensitive to both seismic and magnetic disturbances indistinct segments of a boundary.

Prior art intrusion detection systems have typically used either aseries of seismic point sensors or a single magnetic line sensor todetect intrusion. An example of a system using geophones as seismicpoint sensors is shown in US. Pat. Application Ser. No. 262,888, filedJune 14, 1972. The information available from such systems is limited,and failure of these systems to provide sufficient intelligence todistinguish between noise, far-field disturbances and actual intrusionsmay result in nuisance alarms.

An example of a segmented sensor which can be used to provide bothmagnetic and seismic signals is shown in US. Pat. Application Ser. No.218,102, filed Jan. 17, 1972 now US. Pat. No. 3,747,036. The presentinvention is apparatus which will effectively use magnetic and seismicinformation from a plurality of boundary segments to gain informationwhich decreases the probability of nuisance alarms while increasing theprobability of detecting actual intrusions. The present invention istherefore particularly suited for use with a sensor of the type shown inApplication Ser. No. 218,102.

Two drawbacks of prior art systems have been: (i) their failure toaccurately sense the lack of localization of a disturbance and inhibitintrusion alarm when the disturbance is not sufficiently localized torepresent an intrusion, and (ii) their failure to use information aboutthe impulsive or non-impulsive character of the disturbances to vary thelevel of disturbance required to activate the alarm.

It is therefore a principal object of the present invention to provideintrusion detection apparatus which detects whether or not a disturbanceis localized and inhibits the alarm if the disturbance is notsufficiently localized to represent human intrusion.

Another important object is to provide intrusion detection apparatuswhich determines whether a detected seismic disturbance is impulsive innature and uses the determination to vary the threshold of magneticdisturbance required to actuate an alarm.

Still another object is to provide an improved intrusion detectionsystem usable with signals indicative of both seismic and magneticdisturbances.

Yet another object is to provide an improved intrusion detection systemwhich utilizes signals indicative of the level of disturbances in anumber of distinct segments of a boundary.

SUMMARY OF THE INVENTION These objects are achieved by intrusiondetection apparatus for processing a plurality of sensor signals, eachof which is indicative of the level of disturbances in a distinctsegment of a predetermined boundary across which intrusions are beingdetected. Means for receiving and averaging'each of the sensor signalswith time are provided. Each of the time averaged sensor signals is thenprovided to threshold detection means and array comparison means. Thethreshold detection means detects when one of the averaged sensorsignals exceeds a predetermined amplitude, and generates an activatesignal upon such detection. The array comparison means compares therelative amplitudes of the time averaged sensor signals with one anotherand generates an inhibit signal if these relative amplitudes are withina predetermined range. Alarm control logic for the apparatus responds tothe signals generated by the array comparison means and thresholddetection means to produce an alarm actuation signal at times when saidactivate signal is generated but said inhibit signal is not beinggenerated.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of theinvention will become apparent upon reading the following detaileddescription and upon reference to the drawings in which:

FIG. 1 illustrates the physical configuration of one segment of a linesensor suitable for use with the intrusion detection apparatus;

FIG. 2 illustrates the electrical configuration of a three-segment linesensor suitable for use with the improved intrusion detection apparatus;

FIG. 3 is a functional block diagram of the intrusion detectionapparatus;

FIG. 4 shows illustrative seismic waveforms which might be developed inthe segments of a line sensor of the type shown in FIGS. 2 and 3 inresponse to disturbances created by a human intrusion;

FIG. 5 is a block diagram showing, in more detail, a dual channelseismic and magnetic amplifier used in the apparatus of FIG. 1;

FIG. 6 is a block diagram, illustrating, in more detail, the seismicsignal processing portion of the apparatus;

FIG. 7 is a detailed block diagram of the magnetic signal processingportion of the apparatus;

FIG. 8 is a truth table which illustrates the criteria applied to themagnetic signals by the array comparison portion of the apparatus;

FIG, 9 is a detailed block diagram of the control, combination logic,and output sections of the apparatus.

The improved intrusion detection apparatus has been developed for usewith a sensor providing information about both seismic and magneticdisturbances along a predetermined boundary of a protected area.Although a specific line sensor usable-with this invention is shown inFIGS. 1 and 2, any segmented sensor or combination of individual sensorswhich provides information about magnetic and seismic disturbances in aplurality of specific segments of a boundary would be suitable for usewith the preferred embodiment shown in block diagram form in FIG. 3.

The transducer shown in FIGS. 1 and 2 is a line sensor which takes theform of a line or cable. The transducer of FIGS. 1 and 2 is described indetail in US. Pat. Application Ser. No. 218,102, referred to above. Itis described here only to simplify the task of understanding theoperation of the intrusion detection apparatus of the present invention.

The physical structure of one portion of a line sensor is shown inFIG. 1. The portion shown cutaway layer by layer has a core 10 offerromagnetic material, a first insulative layer 12, a helical winding14, a second insulative layer 16, a set of electrical leads 18, two foreach segment, a third insulative layer 20, a first electrical shieldmaterial 22, a fourth insulative layer 24, a second electrical shield26, and an outer jacket or protective sheath 28.

In one successful embodiment of this sensor, the ferromagnetic materialfor the core was constructed of 19 strands of 0.042 inch Blendalloy25-8005, while the first insulative layer 12 was made of Kapton.Insulative layers 16, 20, and 24 were dual layers, comprising one layerof Teflon and one layer of Kapton. Helical winding 14 was constructed ofAWG 30, Celanese covered, insulated magnet wire. Electrical shields 22and 26 were 0.004 inch thick cylindrical layers of silver. Finally,protective sheath 28 was constructed of extruded polyurethane.

One successful electrical configuration of the line sensor isillustrated in FIG. 2. That figure shows a line sensor 30 having threesegments 32, 34, and 36. Segments 32, 34, and 36 are electricallyisolated. Each segment is made up of an even number of sections, in thiscase eight, connected in electrical series. Two illustrative sectionswhich are a portion of segment 32 are labelled with reference numerals37 and 38. Each pair of sections acts as a magnetic gradiometer andalternate sections such as 37 and 38 have oppositely wound coils 14. Thealternation of oppositely wound sections along the length of sensor 30is indicated by plus and minus signs showing opposite potentials acrossadjacent sections. Also shown in FIG. 2 as two dotted line cylinders arelayers of electrical shielding 22 and 26. The use of a number ofalternate oppositely wound sections in each segment aids in cancellingor rejection of far-field noise while effectively enhancing near-fieldor local effects through a mechanism described in US. Pat. ApplicationSer. No. 218,102, referred to above.

In the line sensor of FIGS. 1 and 2, the disturbance information isobtained in the following way. Ferromagnetic core 10 is strained by eachseismic disturbance. The strain in the ferromagnetic material results inmagnetic field changes due to magnetostriction. The resultant magneticfield changes induce electrical signals in windings 14. Magnetic fieldchanges of a different frequency are caused by movement of ferrousobjects in the vicinity of segments of sensor 30. These magnetic fieldchanges due to magnetic disturbances induce further electrical signalsin windings 14. Thus electrical signals representing both seismic andmagnetic disturbances are generated in the same winding and a mixedsignal indicative of these disturbances is obtained. Since the seismicand magnetic portions of the signal lie in different frequency bands,they may be separated by appropriate filtering.

FIG. 3 shows a functional block diagram of an improved intrusiondetection system built using one embodiment of the present invention.FIG. 3 shows line sensor 30 as a block having three segments 32, 34, and36 separated by dashed lines.

Electrical signals indicative of the combined seismic and magneticdisturbances in each segment of the boundary covered by segments 32, 34,and 36 are represented by labelled arrows directed outwardly from eachof the segments. As shown in FIG. 3, the seismic and magnetic signalsfrom segments 32, 34, and 36 are s (t) and m,(t); s (t) and m (t); and s,(t) and m (t) respectively. Since the portion of the apparatus whichamplifies. filters, and averages the signal from each line sensorsegment is virtually identical to that of the others, only the elementsassociated with segment 32 will be described. The subscripts adoptedabove will apply to the signals from the respective segments throughout.Segment 32 is connected to a signal processing channel generallydesignated 37. Signal processing channel 37 includes a amplifier 42, asampled averager 44, and an averager 46. Amplifier 42 amplifies thecombined signal received from segment 32 and applies appropriatefiltering which essentially separates the seismic and magnetic portionsof the signal from one another. Amplifier 42 has two outputs: a signalrepresentative of the absolute value of the seismic disturbance Is,(t)|;and a signal representative of the negative of the absolute value ofthemagnetic disturbance[m,(t)| The output of amplifier 42 carrying |s,(t)lis connected to sampled averager 44. Sampled averager 44 functions togenerate a normalized pulse at an output labelled P, in response to eachseismic disturbance above a predetermined threshold or level. Inaddition, averager 44 generates a signal at an output labelled A whichrepresents a time average of the seismic disturbances above the samepredetermined threshold. The signal on output A,, is a sampled averagein the sense that only disturbances greater than the predeterminedthreshold are averaged. The other output of amplifier 42 carries thesignal -lm,(t)l to averager 46 which generates a time average of thesignal at output A,,,,. The signal on output A,,, is said to be anunsampled average in that there is no predetermined threshold level thathas to be exceeded by the magnetic disturbances before they areaveraged.

Segments 34 and 36 each have elements which are functionally equivalentto the role of amplifier 42, sampled averager 44, and averager 46 withrespect to segment 32. These equivalent elements include amplifiers 42and 42", sampled averagers 44 and 44", and averagers 46' and 46". Inaddition, the channels processing signals from segments 34 and 36 arelabelled 37' and 37" respectively. Channel 37, associated with linesection 34, generates pulses P level A and level A channel 37",associated with section 36, generates pulses P level A and level A,,,

The pulses at outputs P P and P and the voltage levels present atoutputs A A and A contain seismic information. The pulses at P,, P and Prepresent seismic disturbances above a predetermined threshold. Thevoltage levels at A A A represent the average intensity of the seismicdisturbances. The voltage levels at A,,,,, A and A contain magneticinformation representing the average intensity of the magneticdisturbances. The seismic information is now processed in a seismicmaximum selector 50 while the magnetic information is processed in anarray extractor 60 and a magnetic maximum selector 64.

The seismic maximum selector 50 directs one of the outputs P,, P or Passociated with the sampled average from A A or A which is of thelargest amplitude to the output P. As an example, if the amplitude ofoutput signal A is largest of the three sampled average signals, maximumselector 50 directs the pulses from output P to the output P. The pulsesgenerated at P are applied to the input of a time-between-pulseextractor 56 and a control and combination logic block 58.

The time between successive pulses generated at output P quite clearlyis related to the nature of the disturbance causing the pulses. Forexample, it is known that the human body alone does not generate seismicdisturbances spaced less than about 60 milliseconds apart. This is awell established upper limit upon the speed of human movement. From thisknowledge, it can be determined if a human has caused a seismicdisturbance by determining the period between successive disturbances.If the period is less than 60 milliseconds it is unlikely that a humanis involved. Time-between-pulse extractor 56 performs this function. Itis connected to output P to receive pulses therefrom and generatesanoutput logic signal or pulse at an output labelled IM (for nonimpulsiveor non-human) if it detects or counts av predetermined number of pulsesspaced less than 60 milliseconds from one another.

Since the average levels A A and A will change slowly relative to thefrequency of the disturbance, the pulses from output P will occur ingroups or packets with all pulses in a group associated with the sameline sensor segment and therefore the same source of disturbance(assuming there is a simple source of disturbance associated with a linesection at any one time). Each pulse group is processed by extractor 56to determine whether the source of disturbancesis not impulsive, i.e.,not human. This seismic disturbance information is combined with theinformation obtained from the magnetic disturbance signals.

The averaged magnetic disturbance signals from outputs A,,,,, A,,, and Aare applied to the input of an array extractor 60. The output ofextractor 60 is a pair of outputs labelled BCR and ABR. Array extractor60 compares each of two of the three signals received with a friction ofthe sum of the remaining two. If these two comparisons indicate thateach of the two signals is larger than the sum of the remaining twomultiplied by the fraction, then the logic level of both outputs will beL or low level. In this condition, the double L level signal shouldinhibit the alarm, since it is assumed that far-field effects havecaused the disturbance. The outputs BCR and ABR are applied to thecontrol and combination logic block 58 for precisely this purpose. Afurther discussion of the array extractor response occurs in conjunctionwith FIG. 8.

The magnetic disturbance signals from A A and Aunt a e also applied asinputs to a magnetic maximum selector 64. From the signals received byselector 64, the signal with the greatest amplitude is selected anddeveloped at the output of selector 64. The output of selector 64 isthen applied to the input of an amplitude extractor 68.'Two binarysignal outputs, labelled HT and LT, form the output of extractor 68. Ifthe amplitude of the magnetic disturbance signal selected by selector 64is greater than a first predetermined upper threshold, the logic levelsignals from both the HT and LT outputs will be H" or high. If theamplitude is greater than a second predetermined lower threshold, butless than the upper threshold, the LT logic level will be high while theHT logic level will be low. Finally, if the selected signal amplitude isless than either the upper or lower thresholds, the logic levels at bothHT and LT outputs will be low. The logic signals at HT and LT are alsoapplied as inputs to the control and combination logic block 58.

The output of control and combination logic block 58 uses the logicsignals received from time-betweenpulse extractor 56, seismic maximumselector 50, array extractor 60 and amplitude extractor 68 to generatean actuate signal for an alarm in appropriate circumstances. If bothoutputs of array extractor 60 are L, indicating that the level ofmagnetic disturbance in each segment is within a fraction of that ineach other segment, the two L logic levels act as an inhibit signal toprevent block 58 from generating the actuate signal. If at least oneoutput of array extractor 60 is *H" or high level, then the alarm may beactuated by the proper combination of signals from extractors 56 and 68.When the output of time-between-pulse extractor 56 indicates anon-impulsive (non-human) seismic disturbance, trip of the upperthreshold or HT output of extractor 68 is required to cause an actuatesignal. On the other hand, if no non-impulsive seismic disturbance ispresent, the low threshold magnetic disturbance out put (LT) ofamplitude extractor 68 will be sufficient to actuate the alarm.

If the disturbances meeting the above criteria are sporadic orrelatively discontinuous, an alarm signal will be generated every 3seconds. If the disturbances are relatively continuous (less than about3 seconds apart) an alarm is generated only after 12 seconds ofcontinuous disturbances. in other words an alarm is generated 3 secondsafter the last sufficient disturbance, or after 12 seconds of continuousdisturbances, whichever occurs first. So that the response of the systemto the signals from segments 32, 34, and 36 may be better understood,FlG. 4 shows three signals which represent the preamplified seismicsignals caused by a human intruder crossing one of the end segments ofthe line sensor. Waveforms X, Y, and Z could represent the preamplifiedseismic signals from sections 32, 34, and 36 respectively. Sincewaveform X has the greatest amplitude an intruder is crossing the linesensor segment which produces that waveform. Consecutive sampledaveraging time periods have been designated 1,, t and As indicated abovethese time periods are started by the sampled averagers when apredetermined amplitude is exceeded. A typical time period for sample isabout 250 milliseconds.

The individual elements comprising one embodiment of the system shown inFIG. 3 will now be described in greater detail. Dual-channel amplifier42 of FlG. l is shown in the block diagram of FIG. 5. The signal fromline sensor segment 32 is shown at the left of HO 5 and is labelled linesignal". The magnitude of the combined line signal from segment 32 isincreased by two successive stages of amplification, a pre-amplifier 72and a post-amplifier 74. Post-amplifier 74 includes an active 60-cyclenotch filter which attenuates 60-cycle variations which the combinedline signal may have picked up from internal or external power sources(not shown). The output of post-amplifier 74 is applied to the inputs oftwo filtering networks. The first filtering network comprises aChebyshev low-pass filter 76 followed by a high-pass filter 78. Thesecond filtering network is a Butterworth low-pass filter 80. The outputsignal from filter 78 represents the seismic signals, which typicallyhave frequency components. in the range of 10 to 40 Hz. The output offilter 80 represents the magnetic or low frequency signals, whichtypically have frequency components in the range of 0.05 to 3 Hz. Theseismic disturbance signals from filter 78 are applied to the input of afull-wave rectificationcomponents having the following characteristics:preamplifier .72 with gain of 1.000, frequency range of 0.05 to 100 Hz;post-amplifier 74 with gain of 64; filter 76 with cutoff frequency of 40Hz; filter 78 with cutoff frequency of 12 Hz; filter 80 with cutofffrequency of 3 Hz; rectifier-amplifier 82 with gain of 24; andrectifier-amplifier 84 with gain of 2.5. In that embodiment, the seismicsignal output of rectifier-amplifier 82, designated |s(t)|, variedbetween and +6.75 volts. The magnetic signal output ofrectifier-amplifier 74, designated |m(t)| varied between 0 and 6.75volts. Each ofthe amplifier 42, 42, and 42" of FIG. 1 may be constructedusing the components shown in block form in FIG. 5.

Specific embodiments of the sampled averagers 44, 44', and 44", seismicmaximum selector 50, and timebetween-pulse extractor 56 appear in FIG.6. Since each of the sampled averagers shown in FIG. 6 is identical tothe others; the operation will be explained only once. The componentswhich comprise averager 44 are surrounded by a dashed line block in FIG.6. The seismic signal [s,(t)] from the output of rectifier-amplifier 82is applied to the inputs of threshold detector 90 and an electronicswitch 102. The seismic signal will ultimately pass through electronicswitch 102 only if its level is above a predetermined threshold, forexample, 650 millivolts. If the seismic signal is above this threshold,threshold detector 90 triggers a one-shot multivibrator 94 which in turngenerates a 250 millisecond wide pulse at an output labelled P,. Theother averagers 44' and 44" may also generate pulses at P and Prespectively.

The pulses from outputs P P and P are applied as inputs to a logicswitch 98 contained is seismic maximum selector 50. The same pulses arealso used to gate or enable switches 102, 102, and 102" in theaveragers. Returning to a description of the averager 44, the pulse fromone shot 94 gates the |s,(t)| signal through electronic switch 102 toaverage and hold element 106. Average and hold element 106 is a circuitwhich takes the time average of its input signal over a particularperiod and holds that level until reset. Element 106 has acharacteristic time constant. Its output is the time average of theportions of |s,(t)| which are gated by switch 102. The same is true foreach of the other elements 106 and 106". The outputs of average and holdelements 106, 106 and 106 are labelled A A and A to indicate that eachis the sampled average of the seismic disturbance signal from aparticular line segment.

The signals at outputs A A and A of circuits 106, 106 and 106" areapplied to the seismic maximum selector shown in a dashed line blockgenerally designated 50. More particularly, outputs A A and A areconnected to a maximum detector 110 included within maximum selector 50.Detector 110 generates a gating signal on one of three output lines 111,112, or 113 depending on which of its input signals is detected to havethe largest magnitude.

The gating signal is applied to logic switch 98 as are pulsed fromoutputs P P and P previously described. Depending on the line on whichthe gating signal is present, P P or P, triggers the generation ofrelatively narrow output pulse at an output P of logic switch 98. As anexample, consider the case in which the signal on output A is largerthan that on outputs A, or A, Maximum detector 110 will function togenerate a gating signal on the proper line to gate the associatedpulses from P into logic switch 98 which will effectively direct thepulses from P to output P. In this way, only the seismic pulsesassociated with the line sensor segment with the greatest sampledaverage level of seismic disturbances appear at the P output.

The pulses at P are applied to an input of the control and combinationlogic block 58 and the time-betweenpulse extractor 56. Extractor 56includes a differentiator 114,21 one-shot multivibrator 116, an AND gate118, and a counter 120. The pulses from P are applied to the input ofdifferentiator 114, the output of which triggers one-shot multivibrator116. One-shot 116, when triggered, generates a 60 millisecond outputpulse. The 60 millisecond pulse from one-shot 116 enables AND gate 118so that if a second pulses occurs at P within 60 milliseconds of thefirst, it passes through AND gate 118 and is counted by counter 120.Counter 120 is set to produce a logic output pulse at an output labelledIM after receiving 9 input pulses. The count of 9 is arbitrarily chosen.The counter range might be from 3-30 counts depending upon theparticular application of the system. Thus the generation of a logicpulse by counter 120 means that there have been 9 periods of 60milliseconds or less between successive P pulses which indicates adisturbance not sufficiently impulsive, i.e., of too high a repetitionrate to represent human intruders. Average & hold circuit 106 andcounter 120 are periodically reset by a reset signal labelled Reset Nfrom the control and combination logic circuitry 58. This resetestablishes a time limit for the averaging of elements 106, 106', and106" and prevents accumulation of counts in counter 120 over a longperiod of time as a result of random disturbances.

FIG. 7 illustrates, in more detail, the averagers 46, 46, and 46", aswell as the array extractor 60, magnetic maximum selector 64, andamplitude extractor 68 of FIG. 3. Since each of the averagers 46, 46,and 46 is identical to the others, only averager 46 will be described.Averager 46 comprises an RC network 122, which may have a time constantof approximately 0.62 seconds, and a buffer element 124, which aids inisolating the network output from the remaining circuitry.

The outputs of buffers 124, 124 and 124 are labelled A,,,,, A and A toidentify their placement in the less specific diagram of FIG. 3. Theseoutputs are connected to each of three peak detect and hold circuits126, 128, and in the array extractor 60. Each peak detect and holdcircuit acquires and holds the highest amplitude of the input signalsapplied to it. The peak detect and hold circuits are periodically resetby the RESET signal from the control and combination logic block 58mentioned previously. The outputs of circuits 126, 128, and 130 areisolated from the circuitry that follows by buffer-amplifiers 131, 132,and 134. The outpuput of each of buffers 131, 132, and 134 is applied toone of the divide-by-iive elements 136, 138, and 140. Eachdivide-by-five element provides, at its output, a signal of magnitudeequal to one-fifth of the peak signal received. The outputs of elements136 and 138 are summed by an adder 142 while the outputs of elements 138and 140 are summed in a second adder 144. The outputs of adder 142 andbuffer 134 are then provided as inputs to a comparator 146, while theoutputs of adder 144 and buffer 131 are provided to a comparator 148.The outputs of comparator 146 and 148 are the logic signals at outputslabelled ABR and BCR, respectively.

The operation of array extractor 60 is most easily understood byconsidering an example. Assume the outputs of buffers 131, 132, and 134are 3.8, 4.0, and 4.2 volts respectively. This corresponds to adisturbance condition where all segments of line sensor 30 areexperiencing somewhat similar magnetic disturbances, a conditionindicative of far-field rather than localized disturbances. In thiscase, the outputs of divide-by-five circuits 136, 138, and 140 will be0.76, 0.80, and 0.84 volts respectively, while the outputs of adder 142and 144 will be 1.56 and 1.64 volts. Therefore the inputs to comparator146 are 1.56 volts at the positive input and 4.20 volts at the negativeinput, resulting in relatively negative or low (L) level output signalat ABR. similarly, the inputs to circuit 148 are 3.80 volts at thenegative input and 1.64 volts at the positive input, again resulting ina relatively negative or low (L) level output signal at BCR.

The occurrence of L states at both ABR and BCR can be used by controland combination logic block 58 as an inhibit signal, preventing alarmactuation due to far-field effects. However, if one of segments 32, 34,or 36 develops a magnetic signal substantially greater than the othertwo, at least one of the logic binary output ABR or BCR will changestates. For example, ifthe A, output from line segment 32 issubstantially greater than that from segments 34 or 36, the output ofbuffer 131 will, be substantially greater than that of buffers 132 and134. This results in a voltage at the positive input of comparator 146which is greater than that at the negative input and the signal leveloutput ABR be comes relatively high (represented by H). FIG. 8 containsa truth table illustrating the states of outputs ABR and BCR whichresult from disturbances in single segments or pairs of adjacentsegments as well as the non-detect condition in which far-fielddisturbances are assumed to exist.

Turning to a discussion of the magnetic maximum selector 64 as shown inFIG. 7, the outputs A A and A,,,;, are each connected to one input of amaximum selector element 150, as well as to three inputs of each of aset of three electronic switches 152. Element 150 determines which ofsignals A A,,, and A is of greatest magnitude and generates a gatingsignal on one of three output leads 154, 156, and 158. Output leads 154,156, and 158 are each connected to gating terminals of one of the threeswitches in block 152. One of the switches 152 is gated or enabled bythe gating signal provided via one of the three gating leads andswitches to provide, at output 160, the largest of signals from A,,,., Aand A,,,;,. For example, if the signal from A is the largest, element150 develops a gating signal on one of the output leads, which gatingsignal is applied to the electronic switch connected to A,,,-;. Thesignal from A is thereby switched through block 152 to the input of theamplitude extractor 68.

Amplitude extractor 68 includes two threshold detector elements 162 and164. Each of these threshold detector elements receives as an input theselected maximum signal transmitted via output 160. If the selectedsignal is above a first relatively high threshold level, detectors 162and 164 will both be energized and the logic levels of outputs HT and LTwill both be high or H. 1f, however, the largest of the signals is belowthe high threshold level, but above a second relatively low thresholdlevel. only detector 164 will be energized. For this case, HT will havea low level signal while LT will be a high level. Finally, if thelargest of the signals is below both threshold levels, neither detector162 nor detector 164 will be energized. Both detector outputs willtransmit low level logic signals.

The control and combination logic block 58 which utilizes the signalsand logic levels previously described is shown in some detail in theblock diagram of FlG. 9. The input signals to block 58 are the logiclevel signals from outputs LT, HL BCR, and ABR as well as logic pulsesfrom output 1M and pulses from P.

The signal from output LT is applied to an OR gate 166, the other inputof which is connected to P. The output of OR gate 166 is applied to theset input of flipflop 168. The signal from LT is also the set input of asecond flipflop 170 and as one input of a two input AND gate 172. The P.input is furtQ-r connected to an AND gate 174 which receives the Qoutput of flipflop 171) as a second input. The HT input i s connected toa set input of a third fliptlop 176. The 1M output is connected to theinput of an inverter 178, the output of which is applied to an AND gate180. In a logical sense then, the input signal to AND gate representsimpulsive or human intrusion due to the inversion. Lastly, signals atBCR and ABR are each applied to OR gate 182.

OR gate 166 sets a flipflop 168 which in trn activates a clock or sourceof system timing pulses 184. Clock 184, operated at 128 Hz, drives al4-bit counter 186 used for system time. Counter 186 develops fouroutputs. An output labelled /s SEC transmits either pulses each secondto an input of a 7-bit counter 188. Two outputs labelled 8S" and 4S"overflow every eight and four seconds respectively to provide outputpulses as inputs to a two input AND gate 190. The fourth output islabelled 16S and overflows every half-second to provide one pulse to athree input AND gate 192.

The 7-bit counter 188 in turn has outputs labelled 18" and 25 at whichpulses are generated every one or two seconds. These outputs areconnected as inputs to an AND gate 194. The outputs of AND gates 190 and194 are each connected as inputs to a two input OR gate 196, which inturn has its output connected as one of the inputs to AND gate 192.

The Q and Q outputs respectively of flip-flop 170 are applied to inputsof AND gates 172 and 174, the output inputs of which are connected to Pand LT respectively. The outputs of AND gates 172 and 174 are connectedas inputs of an OR gate 200. The output of OR gate 200 together with theO output of flipflop 168 are applied to another OR gate 204 the outputof which is used to reset counter 188.

The O output of the third flipflop 176 is applied to one input of an ORgate 208. The Q output of a second flipflop is applied to one input ofAND gate 180, whose output is applied as the second input of OR gate208.

Three inputs are required to actuate the alarm. These include the outputof OR gate 182, the output of OR gate 208 and the output of AND gate192. Functionally speaking, a low level signal OR gate 182 representsprotection against alarm actuation due to far-field disturbances, theoutput of OR gate 208 represents an exceeded magnetic threshold (upperor lower depending upon the frequency of seismic disturbances), and theoutput of AND gate 192 represents the system timing control on thealarm. These outputs are applied to a three input AND gate 210. Theoutput of AND gate 210 provides a logic signal to a relay driver circuit212 to generate an actuate signal for a relay 214 which in turn switchespower to the alarm device.

The operation of the circuit may be most easily understood byconsidering an illustrative situation. Assume a situation in which thedisturbances'sensed are both magnetic and seismic. Further assume thatthe level of magnetic disturbances is between the lower and upperthresholds of the amplitude extractor 68, and that the seismicdisturbances are sufficiently impulsive (long enough period betweenpeaks) to represent human intrusion. Also assume that the disturbancesare not far-field, and that the disturbances are relativelydiscontinuous, or greater than 3 seconds between impulses. ln such asituation, the L T will have a H" level, a pulse will be present a P',[M will have a L" level, and a high level signal will be present ateither BCR or ABR.

Initially, flipflops 168, 170, and 176 will be in the state, that iswith the O outputs at a high or H level. Counters 168 and 174 will bereset by the O output of flipflop 168. OR gate 166 sets flipflop 168either by a signal received at LT or P. When flipflop 168 is set, the 0output goes to H" level and actuates clock 184 operating at 128 Hz. TheQ output of flipflop 168 is further applied to an input of AND gate 192.Pulses from clock 184 are received at the input of 14-bit counter 186.Counter 186 generates, at the output labelled Vs SEC", a set of pulses/a second apart which are applied to the input of 7-bit counter 188.Counter 186 develops another set of pulses /2 second apart which areapplied to one input of AND gate 192. Three seconds after beginning toreceive the /s second pulses from counter 186, counter 188 has developedoutput pulses at and 2S, each of which is applied to AND gate 194. Theoutput of AND gate 194 is applied to one input of OR gate 196. The ORgate 196 has its output connected to the last input of AND gate 192.Thus, three seconds after receiving a signal from LT or P, an H" or highlevel logic signal is developed by AND gate 192 and applied to one inputof AND gate 210.

It will be understood that the LT signal also sets flipflop 170, causinga high level or "H" signal at its Q output. The Q output is applied toone mg of AND gate 180. The inverted signal from output lM is applied tothe other input ofAND gate 180. AND gate 180 develops a high leveloutput signal since the seismic disturbance is impulsive. This allowsthe high level signal at the 0 output of flipflop 170 (created by the LTsignal) to reach OR gate 208 and finally AND gate 210. It will beapparent that if the seismic disturbance had been non-impulsive, thehigh level signal created by the LT output would not have been gatedthrough AND gate 180.

The ABR and BCR outputs are connected to the inputs of OR gate 182.Since it has been assumed that the disturbances are not far-field". atleast one of these inputs will be high level. This will provide OR gate182 with a high level output which will be transmitted as the thirdinput to AND gate 210. AND gate 210, being supplied with three highlevel logic signals will transmit a high level signal at its outputwhich will ultimately actuate the alarm.

If seismic and magnetic disturbances are continuous (less than 3 secondsapart) rather than discontinuous (more than 3 seconds apart) counter 188will be reset before the 1S and 28 output signals have both beendeveloped. The resetting of counter 188 which takes place withcontinuous disturbances from P and LT is effected by AND gates 172 and174 in conjunction with OR gates 200 and 204. If a second LT signal isreceived less than 3 seconds after the first, a reset signal isgenerated by AND gate 172, OR gate 200, and OR gate 204. If a second Psignal is received less than three seconds after the first, the resetsignal is effected by elements 174, 200, and 204. If these disturbancesare continuous and counter 188 is reset, counter 186 will eventuallydevelop output signals 45 and after 12 seconds of continuousdisturbance. 1n this case the output of AND gate 190 will substitute forthat ofAND gate 194 at OR gate 196. Thus, at the end of 12 seconds ofcontinuous disturbance, high level signals will be applied to all theinputs of AND gate 192 and an output signal is developed and transmittedto AND gate 210 in a manner previously discussed.

In situations where magnetic disturbances are strong enough to trip the,upper threshold yet the seismic disturbances are non-impulsive, thesignal from HT sets flipflop 176. The Q output of flipflop 176, whichgoes high, is applied to OR gate 208. The output of OR gate 208 isapplied to the one input of AND gate 210 and an alarm is generated. Thisrepresents situations in which the level of magnetic disturbance is sohigh that alarm is desirable, even though the frequency of seismicdisturbances is higher than that normally associated with humanintrusion.

Thus it is apparent that there has been provided, in accordance with theinvention, improved signal processing apparatus for an instrusiondetection system which fully satisfied the aims, objects, and advantagesset forth above. While the invention has been described in conjunctionwith specific embodiments of certain of its elements, many alternatives,modifications, and variations will be apparent to those of skill in theart in light of this description. Accordingly, it is intended to embraceall such alternatives, modifications and variations as fall within thespirit and broad scope of the appended claims.

What is claimed is:

1. lntrusion detection apparatus for processing a plurality of sensorsignals, each of which is indicative of the level of magneticdisturbances in a distinct segment of a predetermined segmentedboundary, comprising:

averaging means for receiving said sensor signals, and

producing a plurality of output signals which are the time averagesthereof;

array extractor means connected to receive said output signals from saidaveraging means and responsive thereto to compare the relativeamplitudes of the signals received with one another, said arrayextractor means generating an inhibit signal if the relative amplitudesare within a predetermined range;

threshold detection means, responsive to said averaged sensor signalsfor detecting when one of said averaged sensor signals exceeds apredetermined threshold amplitude, and upon such detection generating anactivate signal; and

alarm control logic, associated with said threshold detection means andsaid array extractor means,

and operable to produce an alarm actuation signal at times when saidactivate signal is generated by said threshold detection means and saidinhibit signal is not being generated by said array extractor means.

2. The apparatus of claim 1 wherein at least three sensor signals arereceived for processing, said averaging means generates at least threeoutput signals, and said array extractor means receives and comparessaid three output signals.

3. The apparatus of claim 1 wherein said array extractor means receivesat least three averaging means output signals and determines whether ornot any one of the three received signals has a magnitude substantiallygreater or substantially smaller than the other two.

4. The apparatus of claim 2 wherein said array extraction means comparesrelative amplitudes using the criteria mt mt! mid/( l mi) (141112 mtwhere A,,,,, A and A represent output signals from said averaging means,and K is a positive number greater than or equal to one, and uponsatisfaction of both criteria, said array extractor means generates aninhibit signal.

5. The apparatus of claim 4 wherein the criteria used by said arrayextraction means are further defined by selecting K substantially equalto 5.

6. The apparatus of claim 1 in combination with transmission means forreceiving a seismic signal indicative of seismic disturbances along saidboundary;

time-between-pulse means, connected to said transmission means, forprocessing said seismic signal to determine whether the frequency atwhich said seismic threshold exceeds a predetermined threshold level isabove a given value, said time-betweenpulse means generating a logicsignal if said frequency is above the given value; and

control means responsive to said logic signal to increase said thresholdamplitude at which said threshold detection means generates an activatesignal to a higher value.

7. The apparatus of claim 6 wherein said threshold detection meansincludes a first level detector for detecting when sensor signals whichexceed a first predetermined amplitude and generating a first switchingsignal upon such detection;

a second level detector for detecting when sensor signals which exceed asecond, higher predetermined amplitude and generating a second switchingsignal upon such detection; and

an activate signal generator responsive to said first switching signalto generate said activate signal in the absence of said logic signal,and responsive to said second switching signal to generate said activatcsignal in the presence of said logic signal.

8. improved intrusion detection apparatus utilizing seismic and magneticdisturbance information, comprising in combination:

seismic sensor means responsive to seismic disturbances in each of aplurality of locations along a predetermined boundary to produce aplurality of seismic sensor signals each of which is indicative of thedisturbance in a distinct location;

magnetic sensor means producing a signal indicative of the magneticdisturbances in one location along a predetermined boundary;

seismic maximum means which receives said plurality of seismic sensorsignals, and selects the largest average amplitude seismic sensorsignal;

a seismic signal frequency detector responsive to said largest averageamplitude seismic sensor signal to detect whether the frequency ofdisturbances above a predetermined intensity represented thereby isbelow a predetermined frequency level;

logic means responsive to said magnetic sensor means signal to trip andprovide an alarm actuation signal when said magnetic sensor means signalexceeds a first predetermined amplitude; and

control means responsive to said seismic signal frequency detector toadjust the logic means to trip at a second higher predeterminedamplitude in the event that the frequency detected by said seismicsignal frequency detector exceeds said predetermined-frequency level.

9. The apparatus of claim 8 wherein said seismic signal frequencydetector includes a plurality sampled averager elements, each of whichreceives one of said seismic sensor signals and generates at a firstoutput, a pulse each time the amplitude of the seismic sensor signalreceived exceeds a said predetermined intensity, said sampled averagerelement further operable to provide at a second output, a signal whichis the time averageof the amplitude of those portions of said seismicsensor signal received above said predetermined intensity, and atime-between-pulse extractor connected to said first output of one ofsaid sampled averager elements.

10. The apparatus of claim 9 wherein said seismic sensor means comprisesa plurality of independent sensor elements; the center of the areacovered by each element being at least thirty feet from the center ofthe area covered by each other element.

11. The apparatus of claim 10 wherein said seismic sensor means andmagnetic sensor means further comprise a segmented line sensor, havingthree segments,

each segment of which generates a combined signal intative of magneticdisturbances.

1. Intrusion detection apparatus for processing a plurality of sensor signals, each of which is indicative of the level of magnetic disturbances in a distinct segment of a predetermined segmented boundary, comprising: averaging means for receiving said sensor signals, and producing a plurality of output signals which are the time averages thereof; array extractor means connected to receive said output signals from said averaging means and responsive thereto to compare the relative amplitudes of the signals received with one another, said array extractor means generating an inhibit signal if the relative amplitudes are within a predetermined range; threshold detection means, responsive to said averaged sensor signals for detecting when one of said averaged sensor signals exceeds a predetermined threshold amplitude, and upon such detection generating an activate signal; and alarm control logic, associated with said threshold detection means and said array extractor means, and operable to produce an alarm actuation signal at times when said activate signal is generated by said threshold detection means and said inhibit signal is not being generated by said array extractor means.
 2. The apparatus of claim 1 wherein at least three sensor signals are received for processing, said averaging means generates at least three output signals, and said array extractor means receives and compares said three output signals.
 3. The apparatus of claim 1 wherein said array extractor means receives at least three averaging means output signals and determines whether or not any one of the three received signals has a magnitude substantially greater or substantially smaller than the other two.
 4. The apparatus of claim 2 wherein said array extraction means compares relative amplitudes using the criteria Am1 > (Am2 + Am3)/(K) Am3 > (Am2 + Am1)/(K) where Am1, Am2, and Am3 represent output signals from said averaging means, and K is a positive number greater than or equal to one, and upon satisfaction of both criteria, said array extractor means generates an inhibit signal.
 5. The apparatus of claim 4 wherein the criteria used by said array extraction means are further defined by selecting K substantially equal to
 5. 6. The apparatus of claim 1 in combination with transmission means for receiving a seismic signal indicative of seismic disturbances along said boundary; time-between-pulse means, connected to said transmission means, for processing said seismic signal to determine whether the frequency at which said seismic threshold exceeds a predetermined threshold level is above a given value, said time-between-pulse means generating a logic signal if said frequency is above the given value; and control means responsive to said logic signal to increase said threshold amplitude at which said threshold detection means generates an activate signal to a higher value.
 7. The apparatus of claim 6 wherein said threshold detection means includes a first level detector for detecting when sensor signals which exceed a first predetermined amplitude and generating a first switching signal upon such detection; a second level detector for detecting when sensor signals which exceed a second, higher predetermined amplitude and generating a second switching signal upon such detection; and an activate signal generator responsive to said first switching signal to generate sAid activate signal in the absence of said logic signal, and responsive to said second switching signal to generate said activate signal in the presence of said logic signal.
 8. Improved intrusion detection apparatus utilizing seismic and magnetic disturbance information, comprising in combination: seismic sensor means responsive to seismic disturbances in each of a plurality of locations along a predetermined boundary to produce a plurality of seismic sensor signals each of which is indicative of the disturbance in a distinct location; magnetic sensor means producing a signal indicative of the magnetic disturbances in one location along a predetermined boundary; seismic maximum means which receives said plurality of seismic sensor signals, and selects the largest average amplitude seismic sensor signal; a seismic signal frequency detector responsive to said largest average amplitude seismic sensor signal to detect whether the frequency of disturbances above a predetermined intensity represented thereby is below a predetermined frequency level; logic means responsive to said magnetic sensor means signal to trip and provide an alarm actuation signal when said magnetic sensor means signal exceeds a first predetermined amplitude; and control means responsive to said seismic signal frequency detector to adjust the logic means to trip at a second higher predetermined amplitude in the event that the frequency detected by said seismic signal frequency detector exceeds said predetermined frequency level.
 9. The apparatus of claim 8 wherein said seismic signal frequency detector includes a plurality sampled averager elements, each of which receives one of said seismic sensor signals and generates at a first output, a pulse each time the amplitude of the seismic sensor signal received exceeds a said predetermined intensity, said sampled averager element further operable to provide at a second output, a signal which is the time average of the amplitude of those portions of said seismic sensor signal received above said predetermined intensity, and a time-between-pulse extractor connected to said first output of one of said sampled averager elements.
 10. The apparatus of claim 9 wherein said seismic sensor means comprises a plurality of independent sensor elements; the center of the area covered by each element being at least thirty feet from the center of the area covered by each other element.
 11. The apparatus of claim 10 wherein said seismic sensor means and magnetic sensor means further comprise a segmented line sensor, having three segments, each segment of which generates a combined signal indicative of seismic and magnetic disturbances in the location covered by that segment.
 12. The apparatus of claim 11 and filter means operative associated with said line sensor segments for separating the portion of said combined signal representative of seismic disturbances from that portion representative of magnetic disturbances. 